Some Farm Workers Harbor Antibiotic-Resistant Bacteria, Study Finds

WEDNESDAY July 3, 2013 -- A new study has raised more concerns about the widespread use of antibiotics in U.S. livestock.

Researchers swabbed the noses of workers at two types of livestock farms in North Carolina. They found antibiotic-resistant bacteria associated with livestock in workers at industrial farms where animals are kept in confinement and given antibiotics to promote their growth.

The noses of workers who handle antibiotic-free livestock set out in pastures did not contain antibiotic-resistant bacteria, according to the study, which was published July 2 in the journal PLoS One.

The research team was looking for antibiotic-resistant Staphylococcus aureus bacteria, including the tough-to-treat methicillin-resistant S. aureus, known as MRSA.

"This study shows that these livestock-associated strains are present among workers at industrial livestock operations, and that these strains are resistant not just to methicillin, but to multiple antibiotics -- including antibiotics that are used to treat human infections," study corresponding author Christopher Heaney, an assistant professor of environmental health sciences and epidemiology at the Johns Hopkins Bloomberg School of Public Health, in Baltimore, said in a school news release.

S. aureus can cause a range of illnesses in people, from minor to life-threatening skin, bloodstream, respiratory, urinary and surgical-site infections. Like most illnesses caused by bacteria, S. aureus infections are treated with antibiotics, but drug-resistant strains can be especially difficult to treat.

Multidrug-resistant strains of S. aureus bacteria were about twice as common among industrial livestock operation workers as among antibiotic-free livestock farm workers. And S. aureus strains that were resistant to tetracycline -- an antibiotic used in industrial livestock production since the 1950s -- were 19 times more common among industrial livestock operation workers than among those at antibiotic-free livestock farms.

The workers weren't showing signs of infection at the time of the study.

Although the study showed an association between exposure to animals given antibiotics and development of drug-resistant bacteria, it did not prove a cause-and-effect relationship.